Custom in-ear headsets are well-known in the art and used to facilitate one-way or two-way communication between a headset user and a distant talker. The custom in-ear headset may be coupled to a mobile terminal which transmits audio signals to the in-ear headset via a wired or wireless communication channel. During normal operation, a distant housing portion of the in-ear headset is fitted into the user's or wearer's ear canal. This distant housing portion often comprises a loudspeaker coupled to a sound outlet of the distant housing portion so that audio signals received from the distant talker are processed and transmitted to the user's ear canal, or more specifically to an essentially sealed ear canal volume residing in front of a tympanic membrane or eardrum. For receipt of the user's own voice, an important type of custom in-ear headsets are adapted to pick up the user's voice in or at the user's ear canal by sound transmission through the user's tissue and bone structures. The voice pick-up may be effected by a bone conduction microphone in vibratory contact with a wall section of the user's ear canal or an airborne sound microphone having a sound inlet arranged inside the essentially sealed ear canal volume of the user. A distinctive advantage of this type of sound pick up is good suppression of environmental noise in the microphone signal to be transmitted to the distant listener allowing the user's speech to be conveyed with high fidelity and intelligibility even when the user is located in a very noisy acoustical environment.
However, creating effective sound sealing around the housing of prior art in-ear headset devices to block or suppress leakage of environmental noise to the user's essentially occluded ear canal remains a significant challenge. Since an airborne sound microphone inside the user's ear canal is inherently sensitive to airborne sound and any practical bone conduction microphone also has a certain (undesired) sensitivity to airborne sound, acoustical leakage of environmental sound around the housing will decrease the fidelity and intelligibly of the sound picked up. Likewise, effective sound sealing against the user's ear canal is also beneficial if the custom in-ear headset is configured to act as an active hearing protector attenuating environmental sound and noise above a preset sound level to protect the user's hearing.
One obstacle to reach effective sound sealing or sound attenuation is the varying or dynamic geometry or shape of the user's ear canal caused by user activity such as chewing, eating, yawning etc which leads to the formation of a time-varying acoustic leakage path around the housing. Another obstacle to effective sound sealing is user comfort. Even though a very tightly fitted housing geometry, for example a deliberately oversized housing geometry, could provide good sound sealing it has proven to lead to unacceptable wearing comfort by exerting painful pressure on a large portion of the user's ear canal.
For hearing aid housings, where adequate attenuation of acoustical feedback between a hearing aid receiver and microphone often is of concern, it has been proposed to mount soft silicone rings or annular closed cell foam devices around hard shell hearing aid housings. This type of soft sealing devices are intended to provide sound or acoustical sealing of the user's ear canal with acceptable wearing comfort even during the above-described dynamic shape variations of the user's ear canal.
Patent specification U.S. Pat. No. 6,129,175 discloses an earpiece of polyvinyl chloride plastisol to be inserted into a user's ear canal and be compressed or deformed to acoustically seal the ear canal. The nose or the outermost portion of the earpiece comprises a number of deformable and highly flexible discs for the purpose of creating multiple layers of sound blocking and for enhancing comfort.
Patent specification WO 2009/125186 discloses an ear tip or ear plug with a body portion having flexible peripheral rib elements projecting there from to provide a comfortable and secure fit in a wearer's ear. The rib elements (and e.g. also the entire earpiece) are so flexible that they deform against the surface of the ear or ear canal to form an effective seal. The ear tip or ear plug is a generic earpiece, i.e. not one which is custom-made for a particular user.
The present inventors have, however, experimentally demonstrated that utilizing a substantially hard ridge projecting from and circumscribing a distant housing portion of the custom in-ear headset leads to a surprising improvement of the acoustical sealing of the user's ear canal when the ridge is pressed against a relatively soft cartilaginous portion of the user's ear canal. This arrangement of the ridge allows the ridge to contact and displace an annular wall portion of the soft cartilaginous ear canal that is sufficiently small to avoid serious discomfort. This is different from having soft and flexible ridges or other elements that deform against the ear or ear canal.